The invention relates generally to methods and/or apparatuses for production of cyanide salts and by product salts from hydrogen cyanide or Group IA or Group IIA cyanide salts without the use of sodium hydroxide.
Sodium cyanide production has become increasingly important since the late 19th century when a process using cyanide to extract gold and silver from ores was patented. The Beilby process for producing NaCN was predominant in 1891 and produced significant industrial quantities of sodium cyanide until about 1900 when the Castner process superceded it. The Beilby Process consisted of reacting fused carbonates of potassium and sodium with ammonia and carbon:
Na2CO3+K2CO3+4NH3+2Cxe2x86x922NaCN+2KCN+6H2O
The Castner process produced a much higher purity sodium cyanide product by reacting molten sodium metal with ammonia and charcoal. The process became preferred because reagent costs were reduced (sodium is less expensive than potassium).
2Na+2NH3+2Cxe2x86x922NaCN+3H2
Wet processes that react hydrogen cyanide with sodium hydroxide solution superceded both of the above methods. One process (U.S. Pat. No. 2,993,754, Jenks and Linder, Jul. 25, 1961) reports reacting high purity liquid hydrogen cyanide with a concentrated sodium hydroxide solution.
HCN+NaOHxe2x86x92NaCN+H2O
The resulting solution or slurry from this neutralization can be sold as a solution or evaporated, crystallized, dried, and briquetted. Another process (U.S. Pat. No. 3,619,132, H. J. Mann, Nov. 9, 1971) reports directly absorbing HCN containing gas into a sodium hydroxide solution. The resulting slurry or solution can be evaporated and crystallized. The wet processes represent improvements in reagent costs and product purity from the earlier processes.
There remains a need for a process to produce sodium cyanide or other cyanide salts that does not involve the use of caustic soda (sodium hydroxide) as a reagent.
Provided is a method of preparing sodium cyanide and other Group IA and Group IIA cyanide salts. Generally, there are four main embodiments of the disclosed process. These include a two step process using anion exchangers to metathesize cyanide salts; a two step process using cation exchangers to metathesize cyanide salts; a one step process using anion exchangers to directly metathesize cyanide salts; and a one step process using cation exchangers to directly metathesize cyanide salts. xe2x80x9cTwo stepxe2x80x9d processes first convert Group IA or Group IIA cyanide salts, or ammonium cyanide, to an alkali salt using a base such as lime (calcium hydroxide) or other bases, preferably other than NaOH. The subsequent basic cyanide salt is then reacted in an anion or cation exchange apparatus, such that the desired cyanide salt product is formed. xe2x80x9cOne stepxe2x80x9d or xe2x80x9csingle stepxe2x80x9d processes directly produce cyanide salt products without first being converted to a basic salt.
More specifically, a method is provided of making a compound selected from the group consisting of: Group IA and IIA cyanide salts comprising: (a) contacting a reacting substance comprising cyanide ion and a first exchangeable cation with an ion-exchange media containing a second exchangeable ion wherein either the cyanide ion or the first exchangeable cation exchanges with the second exchangeable ion; and (b) if the cyanide ion is exchanged, contacting the ion-exchange media with a composition selected from the group consisting of: Group IA or IIA metal ions and a third exchangeable ion, wherein the third exchangeable ion is exchanged with cyanide ion and whereby Group IA or IIA cyanide salts are formed; provided that if the first exchangeable cation is exchanged, the second exchangeable ion is a Group IA or Group IIA metal. The method may further comprise the step of reacting said reacting substance with a pre-reacting material which contains one or more Group IA or Group IIA elements or ions, or ammonium, producing a reacting substance comprising cyanide and either ammonium or at least one Group IA or Group IIA element, before contacting said reacting substance with said ion-exchange media.
The reacting substance may be one or more of hydrogen cyanide, Group IA cyanides, Group IIA cyanides, or ammonium cyanide. It is preferred that hydrogen cyanide is the reacting substance. The pre-reacting material is preferably calcium hydroxide or calcium carbonate. The Group IA or Group IIA cyanide salt product is preferably sodium cyanide.
The disclosed process may proceed through anion exchange or cation exchange. In the anion exchange process, hydrogen cyanide or some neutral or alkaline cyanide feed solution comprising cyanide anions and one or more Group IA or Group IIA cations is contacted with an anion exchange media; cyanide anion displaces the anion from the anion exchange media and forms a cyanide loaded ion exchange media; the solution containing the feed cation and the displaced anion that was originally present on the ion exchange media is preferably removed; the cyanide loaded resin is contacted with a solution containing a second cation and an anionic counter-ion which displaces the cyanide, forming a solution containing the second cation and the cyanide ions.
The disclosed process may also proceed through cation exchange. In the cation exchange process, hydrogen cyanide or some neutral or alkaline cyanide salt feed solution comprising cyanide anions and one or more Group IA or Group IIA cations is contacted with a cation exchange media; the Group IA or Group IIA cation displaces the cation from the cation exchange media and forms a Group IA or Group IIA loaded exchange media; and a solution comprising the cyanide anion and the displaced cation from the exchange media is formed. The ion exchange media may be regenerated, as known in the art.
A two-step process using anion exchangers is provided, wherein a cyanide gas or liquid composition comprising one or more Group IA or Group IIA cations is contacted with a basic salt solution having a first exchangeable cation. The first exchangeable cation exchanges with the Group IA or Group IIA cation to form a basic cyanide solution. This solution is contacted with an ion exchange media that is loaded with a first exchangeable anion. Cyanide ions exchange with the first exchangeable anion to form a cyanide-loaded ion exchange media. A solution containing a second exchangeable anion that can exchange with the cyanide ions and a second exchangeable cation that can combine with the cyanide to form a desired salt is contacted with the media. Cyanide is displaced from the media and the desired salt solution is formed.
A two-step process using cation exchangers is also provided, wherein a cyanide liquid or gas composition comprising one or more Group IA or Group IIA cations is contacted with a basic salt solution having a first exchangeable cation. The first exchangeable cation exchanges with the Group IA or Group IIA element to form a basic cyanide solution having the first exchangeable cation. This solution is contacted with an ion exchange media that has a second exchangeable cation. The first exchangeable cation exchanges with the second exchangeable cation, forming a cyanide salt solution comprising cyanide and the second exchangeable cation. The media may be returned to its original state by means known in the art.
A one-step process using anion exchangers is also provided, wherein a cyanide gas or liquid comprising one or more Group IA or Group IIA cations is contacted with an anion exchange media containing a first exchangeable anion. The first exchangeable anion exchanges with the cyanide, forming a cyanide-loaded media. The cyanide is removed from the media, if desired, by contacting the media with a solution containing a second exchangeable anion which exchanges with the cyanide ions and a cation which combines with the cyanide to form a desired salt.
A one-step process using cation exchangers is also provided, wherein a cyanide gas or liquid comprising one or more Group IA or Group IIA cations is contacted with an cation exchange media containing an exchangeable cation. The exchangeable cation exchanges with the Group IA or Group IIA anions, forming a desired cyanide solution. The media may be returned to its original state by methods known in the art.
All reactions occur at conditions (such as temperatures, times and pressures) that allow the desired reactions to proceed (effective conditions). It is well understood that effective conditions depend on the particular apparatus used, and determining all effective conditions is well known to one of ordinary skill in the art without undue experimentation. Other reaction conditions may be any value that allows the desired reactions to occur. Effective conditions may be selected so that the reactions occur with a desired rate, for example. The use and operation of ion-exchange media is well known to one of ordinary skill in the art.
The concentration of reactants in the process may be any effective concentration. The concentration of reactants should be such that undesired reactions do not interfere to such an extent that the desired reaction does not occur to the desired extent or with the desired rate. The cyanide-containing solution or gas that enters the process may have any cyanide concentration up to and including saturated solutions. At least an equal molar amount of pre-reacting material as compared to the amount of reacting substance is preferred so that polymerization of the feed solution is avoided. The loading density of the ion-exchange media (i.e., the amount of exchangeable cation or anion present on the media) depends on many factors which are known to the art, such as the particular composition of the media and the presence or absence of competing anions or cations in the compositions which contact the media. Useful loading densities are those which allow the desired reactions to proceed. The useful loading density may be selected so that the reactions occur with a desired rate. In general, the higher the loading density, the faster the exchange reaction will occur, because the anions do not have to compete for exchange sites. The solutions and gases used in the invention may contain substances other than the anions and cations that are exchanged as long as these substances do not prevent the desired reaction from occurring.
One specific preferred embodiment of a two-step method follows. A method of making a sodium, lithium or potassium cyanide solution comprising: reacting a hydrogen cyanide gas or solution with an at least equal molar amount of calcium hydroxide or calcium carbonate for an effective time and at an effective temperature to produce calcium cyanide; reacting said calcium cyanide with an ion-exchange media containing an first exchangeable anion (preferably chloride) for an effective time and at an effective temperature such that said cyanide is exchanged with said first exchangeable anion; and reacting said media with a composition containing one or more members selected from the group consisting of sodium, lithium or potassium together with a second exchangeable anion (preferably sodium chloride), whereby the second exchangeable anion exchanges with said cyanide, producing a solution comprising cyanide and sodium, lithium or potassium. Although this method describes an anion exchange process, a cation exchange process proceeds in an analogous manner, as described herein.
A preferred embodiment of a one-step method is a method of making a sodium cyanide solution comprising: contacting a hydrogen cyanide solution with a cation exchange media which is sodium loaded, for an effective time and at an effective temperature so that hydrogen exchanges with the sodium cation, producing a sodium cyanide solution. Although this method describes a cation exchange process, an anion exchange process proceeds in an analogous manner, as described herein.
The methods of the invention may be used to prepare desired salts of Group IA and Group IIA elements, as described further herein.
As is well known in the art, many substitutions may be made for the particular chemical substances disclosed herein, as long as the chemical substances perform the same function as those they substitute. For example, potassium chloride may be substituted for sodium chloride. Other substitutions are well known in the art and are encompassed by the disclosure herein. All elements of all Markush groups and other chemical groups disclosed in the invention are included individually and as a group, except those that are known in the art or those that are inoperable. All references cited herein are hereby incorporated by reference to the extent not inconsistent with the disclosure herein.